Wafer yield
The proportion of working chips out of all those made on a silicon wafer. Since defects are unavoidable, yield largely determines what a chip costs — low yields on a new node make chips very expensive until the process has matured.
Mechanic: each wafer has random defects (dust, process errors); the larger a chip (die) is, the greater the chance a defect lands on it → larger chips have lower yield. Economics: a wafer costs roughly the same regardless of yield, so few working chips = high cost per chip. That's why new nodes are expensive at first (low yield) and cheaper once matured. It also drives the chiplet strategy: many small dies yield better than one enormous monolithic one. "Binning" partly rescues defective chips by selling them with fewer cores/lower clock. Central semiconductor economics. Related to binning and chiplet yield.